What is the risk to a kidney donor?

Living kidney donation is extremely safe for the donor. It would not be done if it were not, since it is an elective procedure. The low risk is partly because living donors are very carefully evaluated according to standard protocols. If there is any reason donation might be detrimental to the donor, he or she will not be accepted.

The risk of death during surgery is 0.03% (that's three hundredths of 1%), which is comparable to the risk of dying in a traffic accident over a 2-4 year period.

Long-term follow-up studies of kidney donors have shown they maintain excellent health and kidney function. In some studies, in fact, donors have been found to be healthier than the general population. One study found that 20 years after donation, donors had the very same kidney function and rate of hypertension as their siblings who had not donated. Life insurance data shows no difference in lifespan for kidney donors. Another study looked at World War II veterans who had "donated one kidney to their country" due to war-related injuries. Forty-five years later, their risk of decreased kidney function, hypertension or death was no different from their colleagues with two kidneys.

So...kidney donation has negligible risk to the donor, but is life-saving to the recipient. Sounds like a pretty good tradeoff to me.
-Rob